When I opened your file, it's not displaying the MAX value on the axis. I tried it with v10.3 and v10.4. (I don't have v10.2 anymore.) Is it displaying for you?

I tried your basic approach, but still ran into issues: I also should have mentioned that my bar chart is already a dual axis chart. When I added in the new MAX calculation, I got something like this where there's a huge gap between the Dimension values and the actual bar chart: